Teletypewriter secrecy system



r E. O. GAMMELL TELETYPEWRITER. SECRE'CY- SYSTEM Filed March 17, 1943 Zi 50 L zmmm 2 Sheets-Sheet l INVENTCIJR 25X BY, EQGamnQeZZ ATTORNEY June 4, f5

' E. O. GAMMELL TELETYPEWRITER SECRECY SYSTEM Filed March 17, 1943 2 Sheets-Sheet 2 INVENTOR EflGammell Patented June 4, 1946 UNETD 'i'i TELETYPEVRITER. SECRECY SYSTEM Ernest Osmond Gammell, FloralP ark, N. Y.,.as-

signorto American Telephone and Telegraph Company,a corporation of New York ApplicationMarchH, 1943, Serial No. 479,405

typewriter systems which are arranged {or the secret transmission of signals.

It has heretofore been the practice in teletypewriter systems, for example, to obtain some degree of secrecy by specially arrangingthe sending contactsand the receiving code bars of the teletypewriter machines. In such prior secrecy systems each teletypewriter signal or characterwhichusually includes five markinggor spacing pulses inthe ordinary Baudot, code system-undergoes a change in one of its five pulses. For example, the second pulse will be reversed from its normal code .at-thetransmitter from marking to spacing or vice versa. This system is so arranged that a corresponding reversal in the changedpulse is caused to take placeat the correspond ng code bars in the receiving machineso as to reproduce the original signal or character. This. prior secrecy arrangement has the disadvantage, however, that the enciphering or scrambling is uniform and consistent inthat it always takes'place on the same pulsefor example, the second pulseof every teletypewriter signal or character. Due to the uniformity of enciphering or scrambling process the messages may be decoded readily by unauthorized parties. Moreover considerable time ,and expense is;re-

quired to rearrange the sending contacts and the 1 receiving code bars ofthis system so as tobring about a reversal of a different one of the five pulses of the signals or characters. Therefore frequentchanges, in the enciphering or scrambling practiceare impractical. This isa serious difficulty iorrunless frequent changesare made in the cipher, the cipher takes ona pattern ,which is easily detected by one desiring to break the cipher.

One of the objects of the present invention is tomake it possible to change the character of one or more pulses of the Baudot code promptly by a simple circuit translation as distinguished from a mechanical change in the transmitting meohanismand receiving mechanism of the teletypewriter units.

Another object of the invention is to automatically change the character of different pulses of the Baudot code at successive but unequal intervals in a manner determined by the transmitting station, with corresponding. automatic changes at the receiving station so that a receiver will decode the message by making the proper changes in the received pulses.

Still another object of the invention is to provide automatictranslati-ng equipment to produce changes in each of the pulses of the Baudotcode in a desiredorder .at successive but unequal intervals.

A furtherobjectof the invention is to provide meanswhereby the sending operator mayprevent any one -or;;more of the pulses of theBaudot code from being automatically changed in the desired order of succession.

A still further object ofthe inventionis to provide means whereby the sendingoperator may at will changethe-character. of any; pulse, orof any desired numben of pulses of,a Baudot code combination, regardless of the action of any automatic translating, equipment.

The invention also-has as one of its objects to provide'meanswherebywhen any pulseor plurality of pulses of the Baudot code have, been changed in character, either. automatically or at the will of the sendingpperator, the receiving station after receiving the signals can set upa corresponding condition thereat to automatically restore the received message characters to. their original form.

These and other objects of the invention are accomplished by means of the arrangeme nts shown in theaaccompanying drawings and described hereinafter. In the drawings Figure 1 shows the apparatus to beusedat the transmitti s ta oni enq h i s t eme sas t being ,understood that i similar apparatus will be usedat the receiving station for deciphering purposes. 'Fig. 2 is a; schematic layout of a line-circuit having enciphering arrangementsat both the transmittin andreceivingstations. .Eig. 3 is a i uto ;.an --a$ 2 .ate ra tee sh a It also includesa teletypewriter ;instru nent ITY connected in the-line circuit L leadingfrom the transmitting distributor TD to thedistantstation fIfhe instrurnent'fIfTY serves to record the n here messa e, a th n m t ns statio and control theeuecessiveorder in which the ar us im ul e co t fiau cod .W b changed in character. 7 in additionthere isprodeda w t hin e ui m ntSE f de e n t ma ne ian orde in w ic t var puls fil he-fi ldflt co e wi be. r v rsed r otherwis changed in order to introduce a secret cipher into the transmitted message. The switching equipment SE as shown is closely associated with the transmitting distributor arrangement TD, and is controlled by the local teletypewriter instrument TTY by means of a contact Cx operated by the teletypewriter as will be described later.

The sending arrangement TD, as already described, includes the usual distributor D and rotating brush B for successively transmitting to the line L the five units of the Baudot code in a well understood manner. The transmitting apparatus I'D also includes a set of five contacts TC1, TCz, TC3, TC4 and TC5, which are ordinarily operated by means of a tape to determine whether the individual elements of the five unit code will be marked pulses or spacing pulses. It will be understood, of course, that the contacts instead of being operated by a tape may be operated by a key bar transmitter or other means well known in the art.

In the type of system herein disclosed two impulses are transmitted with each character in addition to the five character determining elements of the Baudot code thus making a sevenunit code. One of these additional impulses is a start impulse which precedes the five Baudot code impulses, which are in turn followed by the other additional impulse which is a stop impulse. The stop impulse is always a marking pulse and the starting impulse is always a spacing impulse in the system illustrated. The distributor D includes a solid inner ring connected to the line L and a segmented outer ring having the usual start and stop segments and in addition the five numbered segments. Each of the numbered se ments is connected to an individual one of the tape transmitter contacts T01, T02, etc., so that a marking or spacing condition will be imposed upon the segment in accordance with Whether or not the corresponding contact of the tape transmitter is operated or non-operated. By means of the brush B the start impulse, the five Baudot code impulses and the stop impulse are transmitted from the corresponding segments of the outer ring of the distributor to the inner ring of the distributor and thence to the line Lin a manner well understood in the art.

The brush arm B of the sending distributor D operates continuously to send successions of code combinations for the different characters to be transmitted, and at each revolution of the distributor the controlling sending tape is advanced one step to set up a new combination upon the tape operated contacts TCl-TCS, inclusive. Each teletypewriter instrument, such as TTY, whether located at the sending station for local recording, or whether situated at the distant station for receiving the message is also provided with a rotating receiving selector somewhat similar in, action to the distributor D as is well known. These distributors are of the start-stop type. Their mechanisms are released each time a start impulse is transmitted over the line, come to rest with the stopping impulse, until asucceeding start impulse is received.

With the tape contacts TCi to TCs in the position shown in Fig. 1 each of the five segments of the outer ring of the distributor D will be activated to transmit spacing impulses. This is accomplished in the illustrated circuit by maintaining the conductors connected to each of the segments 1, 2, l3, 4 and 5 open under normal conditions. When any one of the tape operated contacts is moved to the left, however, it will close the conductor leading to the corresponding segment in the outer ring of the distributor. Consequently a marking impulse will be sent, unless by means of the switching equipment SE the impulse is reversed in character for secrecy purposes, as will be described later.

The secrecy switching equipment SE involves five pairs of relays such as TRl and TRi', one corresponding to each of the five contacts of the tape transmitter. lays are unoperated and none of the keys PRKi- PRKs is actuated, none of the Baudot code impulses'sent out by the distributor D will be reversed in character. A key SK is provided which, when operated, actuates a first pair of TR relays in the chain to reverse the character of the first Baudot code impulse set up by the contact T01 of the tape transmitter. If the contact is set to produce a marking impulse, the first impulse actually transmitted will be a spacing impulse. If, on the other hand, the tape contact indicates a spacing impulse, the impulse actually transmitted will be a marking impulse; This means, of course,

that'the code for a different character from that set up by the tape will be sent out.

Associated with each pair of transfer'relays, suchas TR1 and TRi, is a transfer key. Thus the transfer key TKi is associated with the transfer relays TR]. and TRi'. A similar transfer key TK2 is associated with the transfer relays TRz and TR2', which control the reversing of the second Baudot code impulse, and similarly other transfer keys TKa, TKi and TK& are associated with the other pairs of transfer relays.

The transfer relays are so Wired that when the start key SK is operated even momentarily the first pair of transfer relays will be actuated. These relays will remain actuated to reverse the first impulse Baudot code combination sent out, until a special code combination or a group of code combinations is received to transfer the control to the next pair. For example, if the socalled figures code combination is applied-to the teletypewriter TTY in Fig. 1, and this is followed by a particular code combination such as that of the letter S or the letter H prior to a signal combination which will unshift the teletypewriter TTY, said teletypewriter TTY will have its type bar or some part of its type bar operating mechanism arranged to open the contact Cx. The momentary opening of this contact will release the operated pair ofvtransfer relays and will actuate and lock up 'a second pair of transfer relays such as TRz and TR2',. unless the transfer key TKz is operated, in which case the control will be passed to a third pair of transfer relays.

If the second pair of transfer relays TR: and TRz are actuated, they will reverse the second pulse of the Baudot code, and this second impulse will be reversed for each character transmitted until the combination Figs-S (or other preferred character) again occurs as noted above. Thereupon the second pair of transfer relays will be released, and a third pair of transfer relays such as TR: and TR3' are energized to reverse the third Baudot code impulse. In this manner, as successive Figs-S combinations are received, the control wil1-be transferred to successive pairs of transfer relays of the chain. After the last pair of transfer relays have been released by means of a Figs-S combination, the first pair will be again actuated and successive transfers through the chain will again occur. This process will be continued until a clear-cut key CK i op- When these five pairs of reerated to disable all of the pairs of transfer relays. I

- By actuating any one of the transfer keys, for

example -'I'Ka, the corresponding transfer relays.

'IRs and TRs' will be cut out of the chain. This will result in operating the other four pairs. of transfer relays in succession to reverse the 1st, 2nd, 4thand 5th impulses of the Baudot code in: successive and recurring order, without any reversal being made in the third pulse of the code. Also, if desired, any two or more pairs B the fiv'e pairs of transfer relays may be cut out by.

actuating the corresponding transfer keys: of. the TK:group, so that only the remaining pairs oi tran'sfenrelays'will be operated successively and in recurring cycles. 3

Five 'flock-in? pulse reversal keys'PRKi-PRKs, inclusive, are provided. One of these pulse re versal keys corresponds-to each element of the:

Baudot code, and when any one of these keys is operated, the corresponding segment in the outer ringof'the distributor will have its pulse reversed;

This pulse willbe reversed continuously loreacln character to encipher the message in this manner so long as the key remains operated.

It will be understood that when the operator manually controls the reversal of pulses in the Baudot code by operating one of the pulse reverse keys, it willbe necessary to send information of that fact in code or otherwise to the receiving; station. The receiving operator may then make corresponding changes in the pulse reversal keys. at the receiving station to re-invert the code impulse. Such information would normallybe transmitted between message over the same or over other transmission facilities.

It will be understood that at the receiving station, apparatus similar to that shown in Fig. i

will be provided. Therefore the operator will not, only have pulse reversal keys similar to those ofv the PBX group, but will also be provided with five pairs'of transfer relays. These when .set in operation, will be actuated succession and recurring cycles in the same order as the corresponding pairs of relays at the transmitting station through the codes perforated on the tape by the receiving reperforator. This causes a reinversion of any pulse of the Baudot code which was reversed at the transmitting station, that the 'original character of the message willbe recorded on the receiving printer. 7

Whenever a change from one pair of transfer relays to another is made at the transmitting station as a result of a Figs-S combination, the corresponding combination received on the tape at the receiving station is-likewise usedto operate upon the receiving printer to produce a corre sponding change in the transfer relays at the receiving station, with the result that the message will be "rinted in its original form instead of its enciphered form.

Further details of the circuits and apparatus will be clear from a description of the operation, which is as follows:

Assuming that the secrecy switching equipment SE is in the normal position shown in Fig. 1,'thc

sending operator by punching a message in the repe'rfo'rator 'PR'FZ, whiohperforates the. message The receiving equipment asshown schematically in Fig. 2 may consist ofea.

is involved the tape 'Tz" will-be punched in the same manner as the sending'tape T1 which is fed into the transmittinadistributor TDn The reperforated tape T2 atrth'e' receiver is then fed into the equipmentTDaat-the receiving station, which in turn causes the message to be recorded on the teletypewriter TTYz in the usual manner.

' If,.however-, the sending: operator desires to encipher the message, the receiving operator will be notifiedv of that fact; and'before: the enciphere'd message is sent, the transmitting. operator will operate his startingcswitchSK. The. operation of the startingswitch- SK at the transmittingstation illustrated in .Fig..1 completes a circuit from battery through-the .relay 'I'Ri, over contact TKI,

overmake-contact q of switchsSK, through the winding: of: relay: TR1:;..over operated contacts p and o of switchSK; over make contact n of switch SK; over .the normal: contact at the clearing-out switch CK,.-.through.:thev lamp .L and over...the switching contact Cx of'the recording teletypewriterTTY to ground. Relays TR1 andTRiar-e operated overthiscircuit. -1

Contact .b-of relay .TRl completes the locking circuitof relays TRr andTR'i from battery through; the winding. of relay, 'I'R1, over the front contact of armature b of relay TR1, through the windingot .relawTR? 1, over normal contact p of switch It .(assoon as said switch has been restoredto. normal)., .1over normal contact m of said switch SK; over the contact of clearing,- outkey CK, 'throughthe lamp Lp and over contact Cxi to..grouncl. Relays T131 and TR'i are now locked-up and remain locked up so long as the. switch Cx; of. the recording teletypewriter T'IY remains closed.

Before the: relay TR1 was operated the activating icircuitmver segment. No. 1 of the dis tributorD extended fromsaid segment over the backlc'ontact of armature d-of relay TR1, over normalcontact .y of pulse reversal key PRK1 to thetape-operated contact T01 of the, transmitter. If said tape operated contact is in its normal position as" shown, the circuit will continue over its normal contact to the armature c of relay TRl, which inthe released condition of the relay is open. Consequently the segment 1 will be activated to send. an open circuit or spacing impulse. i r

If, however, the-"messagecharacter involved a Baudotmode, combination in which the first pulse is markingathe switch .TCrWould be moved to its. alternativeeposition, whereupon the circuit previously traced would extend over the left-hand contact; of T01 and over the conductor Iuto battery. Under these conditions the first impulse of the Baudot code would be a marking impulse. Thisimpulse would, ofcourse, be preceded as is usual by. a start impulse as the, brush B passes over..,the. start segment, which is open circuited sothat-aspacingpulse is sent to. the.

line L. Asthebrush passes over the segment 1, amarking-dmpulse will bev sent over the brush -B and fthe inner iring, of'the distributor to the line L, if-.-the1switch- TC1' is in'its left or alter-. nativepositionm If-on. the other hand it is in its normal position,.an-iopencircuitorspacing impulse will .besent to the line-L.

.However, when the relay. TR1 is energized as above '-described,.'the first impulse of the Baudot code willbe reversed. Let us first suppose that the character to. be transmittedcalls for a Baudot codeycombination;inswhich the first pulse is a; spacingipulsese-The contact'aTCrwill .then' be in tact c of relay TR1, over contact 'ICr, over normal contact 1/ of key PRKI, over thefront contact of armature d of relay TRi; and through the winding of reverse pulse relay RPRt. to

battery. a

Relay RPR: is energized and its front contact completes a circuit from battery over said front contact, over conductor l2, over the front contact and armature e of relay 'IRi, over conductor 24 to segment 1 of the distributor, and thence over the brush of the distributor to line L. Accordingly the first Baudot pulse sent to the line will be a markingpulse, although the character of the message to be transmitted'called for a spacing impulse. This will result in sending over the line a Baudot code combination corresponding to a different character from that actually punched in the sending tape. Any unauthorized person tapping the line would, therefore, not receive the message transmitted.

Similarly if the character to be transmitted involved a Baudot combination whose first pulse is marking, the contact T01 would be shifted to its left position. The circuit will'now be from battery through the winding of relay PRRt, over conductor ll, over the front contact of-armature d, of relay TRl, over normal contact 1 of key PRK, over contact 'ICi in its left position to conductor l0, and over conductor Ill to battery. No current will flow through the circuit under these conditions, and the relay RPRt will remain deenergized. Consequently no battery will be connected to the first segment'of the distributor D, because segment 1 of the. distributor is connected over the front contact of armature e of relay TR1, and over conductor l2 to an open contact of the relay RPRt. Therefore the first pulse of the Baudot code, which in the case of the character of the message would'have been marking, will now be a spacing pulse, again giving an unauthorized person tapping the line a wrong character.

As long as relays 'IRi and TRi' remain energized, the 2nd, 3rd, 4th and 5th pulses of the Baudot code will not be reversed, but will be sent in normal condition. For example, let us suppose this second pulse is a spacing pulse, and the relay TRz is not energized, as will be the case when relays 'IRi and TRi' are operated. Segment 2 of the distributor D will now be connected over conductor 22, back contact of armature d of relay TRz, normal'contact y of key PRKz, over tape contact 'I'C'z in its right-hand position to the armature c of the relay TRz. As this armature is retracted, an open circuit condition is applied to the segment 2. If,-however, the second pulse is a marking pulse, segment 2 of the distributor D will be connected over conductor 22, over the back contact ofarmature d of relay 'I'R2, over normal contact 3 of key PRK2,

over contact TC'2 in itsleft-hand position, and

thence over conductor to battery. Consequently a marking impulse will be sent to the line L. In oher words, the second impulse of the Baudot code will not be reversed, whether it is a marking or a spacing impulse.

The same holds true for the3rd, 4th and 5th impulses of the Baudot code, as will be evident from tracing the connections from the 3rd, 4th and 5th segments of the distributor over the contacts of deenergized relays TRa, TR or TRa, as the case may be. In other words, as long as the relays 'IRi and 'I'Ri' are energized, the first pulse of the Baudot code will always be reversed, but the others will be sent normally.

Let us assume that the first letter transmitted, afterthe relays TR1 and TRi'areactuated, is the letter A. The five units of the Baudot code for letter A will be mark-mark-space-space-,

space. With the first pulse reversed by reason .of

the energization of relays TR]. and TRi the actual code transmitted will be space-mark-space-spacespace, which is the code for line feed. Consequently at the receiving station, if no deciphering arrangement were provided, the receiver T'I'Ya would be operated, not to record the letter A, but a line feed operation, and this is also the signal that anyone attempting to tap the line would get. However, when the receiving station is equipped with a deciphering arrangement, the signals are perforated on tapes such as T2 and T2 by means of a reperforators RPF: and RPFz' respectively, as shown in Fig. 2.

The received enciphered tape T2 is fed into the transmitter 'ID2 and a duplicate enciphered tape T2 produced by the perforator RPFz' and fed into the transmitter 'I "D2'. With the secrecy equipment at the receiving station set in accordance with the code transmitted by the sending operator prior to the message, the tapes T2 and T2 are thus fed in an identical manner into the two tape transmitters 'I'Dz and TDz' respectively. Tape T2 and transmitter TDQ are used to transmit the enciph'ered message to T'I'Yz equipped with a contact operating similarly to Cx of 'ITY1. Contact RX operates the secrecy switching equipment SE2 at the same position on the tape T2 and in response to the same combination of characters as teletypewriter TTY1 did at the sending station.

Tape Tz'when fed into the tape transmitter TD; at the receiver will not impress upon the associated teletypewrlter TTYz a line feed 818- nal. Instead it will record letter A upon the teletypewriter because of the action of the. switching equipment SE2 at the receiver. This switch ing equipment is substantially identical with that shown in Fig. 1. Since this switching equipment is set at the receiving station in the same manner as equipment TTY1 at the sending station, relays corresponding to TR1 and TR1'.Wi11 be actuated and will re-invert the first Baudot code impulse.

Consequently the Baudot code combination for line-feed, when applied to the tape transmitter TD2 in the code form space-mark-spacespace-space, will have its first'impulse reversed by the switching equipment SE2. It therefore becomes mark-mark-space-space-space, and causes the teletypewriter 'I'IYz to record the letter A.

A11 subsequent characters and stunt signals transmitted will have their first pulses reversed when sent out from the transmitting station, and restored to normal at the receiving station in'a manner similar to that above described, as long as the relays TR1 and 'IRi' at the transmitting station and the corresponding relays at the receiving station remain energized. For example, if nowthe letter G is transmitted, the

code for this letter, which is normally spacemark-space-mark-mark, will have its first pulse reversed so that it comes out mark-mark-spacemark-mark. This is the code for figures-shift, i. e. the code for the stunt operation which causes the printer to shift from letters to figures. The figures-shift signal will then be transmitted over the line and received at the receiving station.

If in the originalmessage the letter Gls fol lowed immediately by the space signal, which is spaces-space-mark-space-space, the'relays TR1 and TRl' at the transmitter will reverse the first pulse of the space signal so that it will be sent out as mark-space-mark-space-space, this being the code for the letter S. Consequently the line L will receive instead of the successive character combinations G-space, the successive code combinations corresponding to figures-S.

The teletypewriter TTY1 at the transmitting station is so arranged that when the combination Figs-S is received, the switch Cx is opened for a short interval, thereby releasing the looking circuit previously traced for the relay TRi at the transmitting station. This causes the relay 'TRi to fallv off and open the circuit of the relay TRi. Relay TRi is slow to release, and therefore a momentary circuit is closed from ground over the back contact of armature a of relay TR1, over the front contact of the armature of relay TRi', over the normal contact of key 'IKe, and through the winding of relay TR: to battery.

Relay IE2 is now energized and at the front contact of its armature b completes a locking circuit (as soon as contact Cx is reclosed) through the winding of relay TRz', over conductor 3 l, over the normal contact m of start key SK, over the normal contact of clear-out key CK, through the lamp L, and thence tog-round over the contact CK of the teletypewriter TTY. Contact Cx was of course closed again as soon as the code combination for character S completed its operations upon the teletypewriter T'I'Y. Relays Tits and IE2 at the transmitting station are now energized, and the former by operating its armatures c, d and e produces'a reversal of the second pulse of the Baudot code for each character thereafter transmitted, until another shift takes place as will be described later.

In the meantime the codes representing figores-shift and character S are transmitted over the line L in succession. ihe reper'forator RPFz at the receiving 'station'periora'tes the code fi ures shift and character S upon the tape T2. The combination Figs-S when fed into transmitter TIDz causes the teletypewriter'TTYz to open a contact Rx. This contact operates the switching equipment SE2 at the receiver in a manner similar-to that just described in the case of the'contact Cx at the transmitting station. This operation releases the relays at the receiver corresponding to TR1 and T81 and energizes and locks up relays at the receiver corresponding to T1322 and TRz. Before this transfer from the one set of relays to the other occurs in the apparatus SE2 at the receiver, the code combinations corresponding to Figs-S which have been already perforated in the tape T2 will be translated by means of the switching equipment SE2 at the receiver into the corresponding code combinations with the first pulse reversed. Since these codes correspond to the letter G followed by the space signal, the letter G will be recorded on the teletypewriter-and will be followed by a spacing operati'on.

After the relays T-Rz and at the transmitter and the corresponding relay at the receiver have been operated, the second pulse of each succeeding character will be reversed at the transmitter, and the corresponding character at the receiver will have its second pulse reinverted to restore the character to its original form. For example, if the letter A, whose code is markmark-space-space-space, is in the original message, itwill be converted at the transmitting station into-the code mark-space-space-spacespace, which is thecode for the letter E. This code for letter E, upon being received at the receiving station, will have its second pulse again reversed, so that it will be sent into the recording teletypewriter T'I'Yz in the form mark-markspace-space-space. Subsequent characters will be similarly enciphered at the transmitter and deciphered at-thereceiver so long as the relays TRz and TR2 at the transmitter and the corresponding relays at the receiver are energized at the proper times.

However, if in the course of the transmitted message the letter B occurs and is followed by the letter U, another shift in the enciphering arrangement will take place. The code for the letter B is mark-space-space-mark-mark, and by reversing the second pulse it comes out markmark space-mark-mark, Which it will be remembered' is the code combination for figures shift. The letter U, whose code is mark-mark-markspace-space, will have its second pulse reversed, and will come mark-space-mark-space-space, which it will be recalled is the code combination for the letter S. Thus we will again transmit into the teletypewriter TTY1 the'comblnation figures-S to again open the contact Cx of said tele typewriter T'I'Yz'. The code combination figures-S will also be transmitted over the line L to reperforator RPFaas will be'described later.

The opening of. the contact Ox at the transmitter will release the locking circuit to the relay TRz, which'in turn opens the circuit for the relay TR2'. By reason of thefact that the latter is slow-acting, however, a momentary circuit is closed from ground over the back contact of armature at of relay TR2, front contact of relay TRz', over the normal contact of the key 'IKs, and through the windingof relay 'I'Rsto battery. Relay TR: is energized and is locked up through the winding of relay This" and, over the contact Cx of the teletypewriter. This contact having been opened only momentarily, is now closed. Relays TR3 and 'I'Rz' are now energized, and-so remain until a new figures-S combination occurs'in the teletypewriter TTY1. The relay TR; through the make contacts of its armatures c, d and e reverses the' third pulse of each succeeding Baudot code transmitted, and'this'condition continues so long as relays TR: and TM remain energized. A corresponding operation of Rx takes place at the receiving station with a similar transfer of the reversingoperation from the second to the third impulse. When similar successive operations of Cx and Rx occur, the succeeding relays are operated in their turn in a similar manner to that above described.

Sooner or later, with the apparatus at both transmitter and receiver advanced to reverse the 5th pulse, a new combination of letters or other signals will occur, which, when their fifth pulses have been reversed, :will cause the combination figures-S to be regarded on the 'teletypewriter TTY1 and transmitted over the line L to the reperforators RPFz and RPFz The momentary opening of the contact CK releases the relay IE5 and closes a momentary circuit from ground over the back contact of armature a of relay TRs, over the front contact of slow release TRa, which has not yet released, over conductors 32 and 33, over the normal contact of key TKi, and through the winding of relay 'I'Ri to battery. Relay TR; will be energized and will be locked up through the winding of relay TR1' over a circuit previously 1 l traced to again cause the reversal-of the first pulse of each Baudot code. Asimilar action will take place at the receiver during the deciphering operations to shift from the fifth pair of transfer relays to the first pair of transfer relays and reverse the first pulse of each Baudot code.

As subsequent Figs-S combinations occur the energized set of transfer relays will be de= energized and the next set actuated at both transmitter and receiver, so that the cycle of transfers already described is repeated. This condition continues until the transmitting operator operates the clear-out key CK. By holding the key CK operated until the slow-release relay of the transfer combination is released, all transfer re lays at the transmitting station will be deenergized, and no pulses of the insuing Baudot codes will be reversed. This operation will normally occur at the end of a message, and the operator will then send an agreed signal to apprise the receiving operator that the coding apparatus is not thereafter to be used. Thereupon the receiving operator will operate the key corresponding to CK and release the transfer relays which are energized at that time, thus restoring the receiving apparatus to normal. 1

In the description above given all five sets transfer relays are operated in succession, but the lapse of time after one pair of relays has been operated until a succeeding pair has been operated varies, and is determined by the fortuitous occurrence of certain character or signal codes in the message after it has been enciphered. This, of course, increases the difliculty of breaking the cipher. However, if desired, further variations in the shifting of the cipher may be introduced by excluding certain pairs of transfer relays from the chain. This exclusion is accomplished by the transfer keys TK1TK5, inclusive.

If, for example, the transfer key TK1 is moved to its alternate position so that the spring rests upon the right-hand contact, then the opera tion of the start key SK will not actuate relay 7 'IRi but will complete a circuit for the relay 'I'Rzz as follows: from battery through the winding of the relay TRz, over the normal contact of transfer key 'IKz, over the alternate contact of key TK1, overconductor 33, over make contact q of key SK, through the winding of relay TRI', through contacts 72 and o of key SK. over make contact 12 of said key, and thence by a circuit previously traced to ground over the contact Cx. Relay TRi' is released after key SK is restored to normal.

In the meantime relay 'I'Rzz operated by this circuit locks up over its contact b, through the winding of relay 'I'Rz which now operates. The transfer relay TRz thus acts to reverse the second pulse of each Baudot code until the FigsJ-S combination occurs and momentarily opens the contact Cx- This releases the transfer relays TRz and TRz and energizes relays TRs and 'IRa. In this manner the control is shifted from the second pair of transfer relays to the third. As later Figs-S combinations occur control passes from the third pair to the fourth, from the fourth to the fifth, and from the fifth back to the second, etc.

Various other combinations may be set up. For example, if the key TK3 is shifted to its alternate position with key 'I'Ki restored to normal, the operation of the start key SK will energize the first pair of transfer relays TRi and T31. When the next Figs-S combination occurs, these relays will be restored to normal and relays 'IRz and T32 will be operated. When the following Figs-S" combination occurs and relay 'I'Rz is deenergized, a momentary circuit is closed from ground over the back contact of armature a of relay TRz, over the front contact of relay 'IRz (which is slow to release), over the spring of key TKa resting on its right-hand contact, over the spring of key TK4, resting on its left-hand contact. and through the winding of relay Titto battery. Thus the second pair of transfer relays are released, the third pair is skipped, and the l fourth pair is operated.

It will also be obvious that two or more pairs of transfer relays may be eliminated by operating a corresponding number of the transfer keys. For example, if transfer keys 'IKa and TK4 are operated, then the control will be exercised by thefirst pair of transfer relays, then by the second pair, and third by the fifth pair, after which it is returned to the first pair.

It will be understood that whenever the send- .ing operator decides to eliminate any pair of 7 transfer relays or any group of transfer relays, information must be transmitted to the distant station in code to that effect, so that the corre sponding changes in the switching equipment at the receiving station will be made. This, of course, will usually be done between messages, although by prearranged understanding this .information could b included in the body of a message being transmitted.

By means of the keys PRKl-PRKS, inclusive,

the sending operator may at will (after having first operated the clear-out key CK) arrange to reverse any pulse of the Baudot code. For example, suppose the sending operator operates the key PRKZ. Then, if the tape contact TCz is in its normal or right-hand position, as is the case when the second pulse of the character code is a spacing signal, a circuit will be closed from ground over make contact of spring a: of the key PRKz, over tape contact TCz in its right-hand position, over make contact of spring 1/ of key PRKz, and then over conductor l4 and through the winding of relay RPRi to battery. The operation of relay RPRI completes a, circuit from battery over conductor [0, over the front contact of relay RPRI, over conductor 13, over make contact of spring 2 of key PRKz, and over conductor 22 to the second segment'of the outer ring of the distributor D. This causes a marking signal to be sent for the second element of the Baudot code instead of a spacing signal. In other words, the second pulse of the Baudot code is reversed. V 7

If on the other hand tape contactTCz is in its left-hand or marking position, as would be the case when the second element of the desired code is a marking pulse, the circuit previously traced for the relay RPRI will be open at contact TCz. Consequently battery will notbe applied to the second segment of the distributor over the circuit previously traced, said circuit being open at the contact of relay RPR. The second element of each code transmitted will be reversed as'long 'as the key PRK2 remains operated. 1 r

In a similar manner if key PRKi is operated and the contact T04 is in its right-hand position, a circuit will be completed for the'relay RPR: from ground over make contact a: of key PRK4, right-hand position of tape contact T04, make contact 11 of key PRK4, and over conductor I 4 to the winding of relay RPRI. Said relay at its front contact connects battery to the conductor l3, and thence over make contact 2 of key PRK4, and over conductor 24 to the fourth segment of the distributor, thus sending a marking impulseinstead of a spacing impulse. If, however, the tape contact TC4 is in its left-hand position, the circuit above traced for relay RPRI will be held open at said tape contact T04, and no battery will be applied to the fourth segment of the distributor. Hence a spacing signal will be sent instead of a marking signal.

It will be evident that the sending operator upon operating any one of the PRK keys, must apprise the receiving operator by a suitable code what combination is to be used, so that the receiving operator may make similar changes in the receiving equipment. When the PRK keys are used as above described the cipher will not be changed automatically, as is the case with the transfer relays, but can only be changed when the sending operator chooses to do so.

In the arrangement shown in Fig. 2 enciphering by means of transfer relays is shifted automatically from one set of transfer relays to another whenever a certain combination of signals appears in the enciphered message. If desired, however, this shift from one set of transfer relays to another may be controlled automatically by means of a separate tape, as shown in Fig. 3. Here the settin of the transfer relays in the equipment SE1 is controlled by special character or other code combinations punched in a cipher tape T1. The message to be sent is perforated in the tape T1, and transmitted in an enciphered form determined by the setting of the transfer relays in the equipment SE1 to the perforator RPFZ, which perforates the tape T2 in accordancewith the enciphered message. When the tape T2 is fed through the transmitting distributor the switching equipment SE2 (which is set to correspond to the equipment SE1 under the control of a cipher tape T2 like cipher tape T1) will decipher the message and cause it to be printed on the teletypewriter 'I'I'Yz in normal form.

In order to shift the control from one set of transfer relays to another at each station. the cipher tapes T1 and T2 are previously prepared. These tapes may have punched in each of them either a random succession of characters or a single character which is repeated until such time as it is desired to shift from one setof transfer relays to another. Wherever it is desired to shift the control, the combination Figs-S will be punched in the tapes. and when this com bination is impressed upon the teletypewriter 'TTYI', the latter will operate its contact corrcsponding to Cx and cause a shift to the next set of transfer relays in the equipment SE2. The similar tape T2 provided at the receiving station operates the teletypewriter T'I'Yz. Whenever the latter receives the combination Figs-S" or any other combination that is decided upon) it will open its contact Rx to shift the control in the switching equipment SE2 from one pair of transfer relays to the next.

The message originally impressed upon the tape T1 will thus be sent over the line L in enciphered form. but when fed through transmitter TDz will be deciphered and restored to its original condition. The tapes T1 and T2 are, of course. punched so that the transfer combination, such as "Figs-S will occur at different intervals of time and the random characters which occur in between these intervals on the tape will be printed on the teletypewriters T'IYi' and T'I'Yz'. However, as these characters are merely punched in the tape to fill in the space between shifting combinations, they have no meaning and may be chosen arbitrarily. Consequently the printing of these characters on the teletypewriter above referred to may be ignored.

It has been shown in connection with the arrangement of Fig. 1 that desired pulses of the Baudot code can be reversed by using a relay RPRt under the control of the several sets of transfer relays, or by means of a relay RPRl under the control of selected lock-in reverse pulse keys PRKI to PRKs, inclusive. In Fig. 4 an alternative arrangement is disclosed which simplifies both the apparatus and its operation, by eliminating the relays RPRt and RPRi entirely, by reducing the number of contacts on the transfer relays and on the lock-in reversal pulse keys, by simplifying the circuit and in other respects. In this arrangement it is possible also to reverse more than one pulse in each character combination.

In Fig. 4, instead of having a single start key SK, individual start keys SKr to 5K5, inclusive, are provided, one for each set of transfer relays. This enables the attendant, by operating the start key corresponding to a particular set of transfer relays, to start the pulse reversals for any given series at any desired pulse of the code. In Fig. 1 the successive reversals always start with the first pulse.

By means of these individual starting keys the attendant may also cause reversals of any two or more pulses of each Baudot code. To do this it is only necessary to operate simultaneously the starting keys corresponding to the transfer relays controlling the pulses which it is desired to reverse. When a plurality of sets of transfer relays are thus operated to reverse, for example, the second and fourth pulses, the circuit of Fig. 4 operates to transfer the reversal control, in response to ffigures-S combination, to the next corresponding pair of pulses. For example, the control is shifted from the second and fourth to the third and fifth impulses, then to the fourth and first, then to the fifth and second, etc. In the arrangement of Fig. 1 it will be recalled that in order to produce such a dual control it was necessary first to operate the transfer keys 'IKi, TKa and TK: and then operate the starting key SK to actuate the fourth set of transfer relays. Then the transfer keys TKz and TK; had to be restored to normal, leaving the transfer key TK1 still actuated, whereupon when the start key SK was again actuated to set a second pair of transfer relays into operation.

The details of the circuit arrangement of Fig. 4 will be clear from the following description of its operation. Assuming first that no one of the five sets of transfer relays are operated and that none of the lock-in pulse reversal keys PRK1 to PRKs are operated, it will be evident that under these conditions the message will be transmitted in normal code combinations without being enciphered by any pulse reversals. For example, as the brush arm B of the distributor D passes over its No. 1 segment, the line L wi l be connected over the inner ring of the distributor, thence over the brush B to segment No. 1 of the distributor, and over conductor 2! to the tape contact 'IC1. If the first pulse is a spacing pulse the tape contact T01 will be in its right-hand position and the circuit will be continued over said contact and over the normal contact of spring 3 of key PRKr to the front contact of armature c of relay 'IRi. As the relay TRi I is not energized, the front contact of said armature c is open and consequently an open circuit first pulse of the code: combination is a markine pulse. the-tape contact 'ICi will be in its-left hand position, and the circuit; will-be. extended over the normal contact .of spring. cof key PRKi, over theback contact of armature c of, relay TRi. and thence over conductor 49 to battery. Under these conditions a marking-impulse is transmitted .to the line L.-; The first .pulscris consequently not reversed.

' Similarly, as 'thebrushwpasses .o-ver'the, second segment of the distributor, if' neither thetransfer relay 'IRz nor thekey PRlKzzisac-tuated, an open circuit will be transmitted to t'he line-when the tape-contact TCz is in its right-hand: or spacing position, whereas if it is inrits le'fthand'ormarkin position; battery willbe connected to the line. Hence the secondiinpulse will not be reversed. andunder the conditions assumed the remaining pulses are also sent normally.

If it is desired to encipher themessage the operator may cause the first. pulseto. be reversed by operating the start key K1, thus energizing transfer relays TRrand. 'I'Ri' in series over an obvious circuit extending over the'make contact of the start key 8K1 and over the contact CX of the teletypewriter TTY. When .thus actuated relays TRl and TRi are locked up in series over the front contact of armature b of relay TRI and over the contact CK of the teletypewriter TTY.

Under "these c0nditions,:if the tape contact T01 is in its right-hand position, as would be the case when the first pulse of the enciphered Baudot code is a spacing pulse, the circuit from th'efirst segment of the distributor will be extended over the right-hand contact of tape contact -TC1, over the normal contact of spring y of key PRKi, over the front contact of armature c of relay TRl (which is now pulled up) and thence over con- ,ductor ll to battery. Consequently .a marking pulse will be transmitted to-thelinelnstead of. a spacing pulse. If, howeventhe, tape contactTci is inits left-hand or markin position, the circult from the first segmentof thedistributorwill be extendedover said contactand overnprmalmake contact of spring 2 of key PRKi to the back contact oi. armature c of relay 'IRi. Asthis. relay pulledup the circuit is Qpenatthisp int and a spacing pulse instead of a marking] pulse is sentto the'line L. a 1

Thu the first pulse oteach .Baudot code will continue tolbe reversed until a ..iigures-.S;.com bination is received. Sucha combination will cause the telctypewriter TTY to ..openf .the contact Cx, thereby unlocking transferrelays TRI and TRi'. A momentary circuit is now establish'ed from ground over the-back contact of armature .a of relay 'lfRi, over the front contact of relay TRY (whicheisi. slow .to releaseqsoithat its armature has not yetv fallen off) and thence over the normal contact oiikey TKaand through the Winding of relay TRztobattery. Relay is operated and locked up inseries with relay TRz' over an obvious circuit extending over the front contact of armature b of relay 'TRz andthe contact CX of the teletypewriter. TTY, which has again closed. With relay TR]. and .TR now.deenergized and relays TBzandTRz' operated, the second pulse of the Baudot codewill be reversed and this will continue, untilin response to another figures-S combination, the contact .Cx is again opened, when relays TRzand TRz' will be released and relays TRs and PR3 will in turn. be actuated and locked up. 1 In this manner the transfer relay sets are operated in succession, and

when th'e-lastset is operated and then-again released .the first set will be. operated and theproc ess repeated just as in the case of Fig- 1.

Instead of starting the enciphering operation by reversing the first pulse of the Baudot code, the process may be started on any other desired pulse. For example, if it is desired to start the process on .the third pulse the start key SK: is

:operated and th'isenergizes relays TR: and TRa', which are locked up to reverse the third pulse of each successive Baudot code until the contactCsis subsequently opened in response to a fflgures-S combination. This releases the third .oftransfer relays and causes relay TR; to be operated over the back contact of armature a of relay TRyand the front contact of'slow release relay TRa'. Relay TR4 now locks up in series with relay TR-4', thereby reversing the fourth pulse. The next time the contact G; is opened the fourth set of transfer relays will be released and the fifth set will be operated. When the contact Cx is again released the fifth set of transfer relays will be released and the relay TR1 will be operated over. a circuit extending over the back contact of armature a of relay TR5, front contact of the armature of slow release relay TRs, and over conductor '32 to the winding of relay TRI, which operates and locks up in series with relay 'IRi' to reverse the first pulse, etc.

If it is desired to reverse two pulses of each Baudot code, for example the second and fourth, start keys SKz and SK4 will be actuated, thus energizing relays T132 and TRz' in series and relays 'I'R4 and 'I'Ri' in series. The circuit of these two parallel sets. of transfer relays is extended over a common conductor 3! and over the clearout key CK to ground over contact CX. All of these relays will be lockedup so that the second and fourth Baudot pulses will'be reversed in each successive code combination until in response to a figures-S combination the contact Cx is momentarily opened, when the second and fourth sets of transfer relays will be released. The release of the relay TRz' causes relay 3R3 to beenergized over an obvious circuit and locked up in series with relay TRa. Likewise the release of relay PR4 causes relay 'I'Rs to be energized over an obvious circuit and locked up in series with relay 'IRs. Both sets ofrelays are connected in parallel through a common circuit extending over conductor 3'! and over the contact Cx to ground. The third and fifth pulses of successive Baudot codes will now be reversed until the next opening of the contact Cx occurs, when thecontrol will be transferred from. the third and fifth sets of transfer relays to the fourth and first sets.

'When these two sets are released the control is next transferred to the fijfthand'second sets or transferrelays, etc;

Itwill also be evident that'more than two pulses of the Baudot'codemay be'reversed; For example, by operating start keyssKi, S143 and SKs the first, third and fifth sets of transfer relays of a given combination of a Baudot code may be reversed, by operating the proper lock-in pulse reverse key of the group PRK1 to PRKs, inclusive. For example, if the key PRK1 is operated, the circuit from the first segment of the distributor will be extended over the spacing contact of the tape-contact TC1, over the make contact of spring 1/ of PRK1, and thence over conductor 40 to battery to send a marking impulse instead of a spacing impulse. If the tape contact is in its marking position the circuit will be extended over the lefthand contact of tape contact TC1 to the spring .2, at which point the circuit will be open, thus sending a spacing impulse to the line instead of a marking impulse.

It will be obvious that if, for example, keys PRK1 and PRK: are operated at the same time, both the first and third pulses will be reversed by said keys. Likewise if the keys PRKz, PRK4 and PRKs are operated at the same time, the second, fourth and fifth pulses will be reversed, etc.

It will be noted that further variations of enciphering code combinations may be obtained by using :both the transfer relays and the lock-in pulse reversal keys. For example, suppose the sets of transfer relays are arranged to operate in successive order to transfer the control of code reversals from the first set to the second, from the second to the third, then to the fourth, etc., as successive figures-S combinations occur to open the contact Cx. .If at the same time the key PRKz is actuated, the enciphering of the code combination will be varied. When the first set of transfer relays is operated the first pulse will be reversed by said transfer relays. The second pulse is controlled by the key PRKz and is therefore reversed by the key, notwithstanding the fact the second set of transfer relays is not operated at this time. Under these conditions both the first and second pulses of each code combination woud be reversed until the contact Cx is opened in response to a figures-S combination. This releases the first set of transfer relays and operates the second set of transfer relays. Under these conditions the first pulse will not be reversed because the first set of transfer relays is released. With the key PRKz and the second set of transfer relays operated, only the second pulse of each code combination will be reversed but this reversal is determined not by the operated second set of transfer relays but by the second key PRKz. When the next figures- S combination occurs the second set of transfer relays will be released and the third set of transfer relays operated. Under these conditions, the key PRKz being operated, the second and third pulses will be reversed, th former under the control of the key PRKz and the latter under the control of the third set of transfer relays.

It will be understood that the transfer keys TK1 to TKs inclusive operate as in Figure 1 to omit any desired transfer relays from the chain so that the pulses corresponding to the omitted transfer relays will not be reversed.

Thus it will be seen that more varied enciphering arrangements of code combinations may be set up with more disturbing efiects upon an unauthorized teletypewriter connected to pick up signals from the line L.

While this invention has been disclosed in certain specific arrangements which are deemed desirable, it will be obvious that the principles herein set forth may be embodied in many other organizations widely different from those illustrat- 18 ed without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, means responsive to the occurrence of certain Baudot code combinations to encipher a message by reversing the electrical character of any desired one of the pulses of each of a. number of successive Baudot code combinations before the code combination is transmitted, the corresponding pulse whether marking or spacing being always reversed in all successive code combinations until a different enciphering reversal is setup, and means responsive to the occurrence of certain Baudot code combinations to restore the pulse previously reversed to normal and to reverse another pulse of each of a different number of successive Baudot code combinations.

2. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitt'ed, means responsive to the occurrence of certain Baudot 'c'o'de combinations to encipher a message by reversing the electrical character of any desired one of the pulses of each of a number of successive Baudot code combinations before the code combination is transmitted, the corresponding pulse whether marking or spacing being always reversed in all successive code combinations until a dilferent ciphering reversal is set means responsive to the occurrence of certain Baudot code combinations to restore the pulse previously reversed to normal and to reverse another pulse of each of a different number of successive Baudot code combinations, and means at a receiving station operating on a particular pulse of a Baudot code combination which is reversed at a transmitting station to restore said pulse to normal and thereby to cause the corresponding character or other signal to be received in deciphere'd form.

'3. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, and means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession, thereby successively enciphering further messages or parts thereof in other forms.

e. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encirpher a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession, thereby successively enciphering further messages or parts thereof in other forms, and means at a receiving station operating on a particular pulse of a Baudot code combination which is reversed at a transmitting station to restore said pulse to normal and thereby to cause the corresponding character or other signal to be received in deciphered form.

5. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, and means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession, thereby suc I cessively enciphering further messages or parts thereof in other forms, the time interval between such successive shifts of reversal control arbitrarily varying in accordance with fortuitous recurrence of said certain Baudot code combinations.

6. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, means responsive each time certain Baudot code combinations ocour to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession, thereby successively enciphering further messages or parts thereof in other forms, the time interval between such successive shifts of reversal control arbitrarily varying in accordance with fortuitous recurrence of said certain Baudot code combinations, and means at a receiving station operating on a particular pulse of a Baudot code combination which is reversed at a transmitting station to restore said pulse to normal and thereby to cause the corresponding character or other signal to be received in deciphered form.

7. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted,means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part there'of'in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession,

thereby successively enciphering further messages or parts thereof in other forms, and means operating in response to further occurrences of said certain Baudot code combinations to again cause transfer of reversal control through said devices in the same succession.

8. In a secrecy system, means to translate messages into Baudot code combinations represent-' ing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession, thereby successively enciphering further messages or parts thereof in other forms, means operating in response to further I occurrences of said certain Baudot code combinations to again cause transfers of reversal control through said devices in the same succession, and means at a receiving station operating on a particular pulse of a Baudot code combination which is reversed at a transmitting station to restore said pulse to normal and thereby to cause the corresponding character or other signal to be received in deciphered form.

9. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable When operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated deivce and to transfer pulse reversal control to other of said devices in succession, thereby successively enciphering further messages or parts thereof in other forms, and means operating in response to further occurrences of said certain Baudot code combinations to again cause transfers of reverse control through said devices in the same succession, the time interval between such successive shifts of reversal control arbitrarily varying in accordance with fortuitous recurrence of said certain Baudot code combinations.

10. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causme one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to the otherof said devices in succession, thereby suc-..

cessively enciphering further messages or parts thereof in other forms, means operating in response to further occurrences of said certain Baudot code combinations to again cause transfers of reversal control through said devices in the same succession, the time interval between such successive shifts of reversal control arbitraril-y varying in accordance with fortuitous recurrence of said certain Baudot code combinations, and means at a receiving station operating on a particular pulse of aBaudot code combination which is reversed at a transmitting station to restore said pulse to normal and thereby to cause the corresponding character or other signal to be received in deciphered form.

11. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession, thereby successively enciphering further messages or parts thereof in other forms, and means to prevent the operation of any of said devices at will so that transfers of control will take place successively among only the devices not prevented from operation, thereby preventing reversals of certain of the pulses of Baudot code combination.

12. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing the corresponding pulse of each Baudot code combination before the code combination is transmitted, means causing one of said devices to control the reversal of the pulse controlled by it in a plurality of Baudot code combinations to thereby encipher a message or part thereof in one form, means responsive each time certain Baudot code combinations occur to defeat control by a previously operated device and to transfer pulse reversal control to other of said devices in succession, thereby successively enciphering further messages or parts thereof in other forms, means to prevent the operation of any of said devices at will so that transfers of control will take place successively among only the devices not prevented from operation, thereby preventing reversals of certain of the pulses of Baudot code combinations, and means at a receiving station operating on a particular pulse of a Baudot code combination which is reversed at a transmitting station to restore said pulse to normal when received and thereby to cause the corresponding character or other signal to be received in deciphered form.

13. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each of the five pulses comprising the Baudot code and capable when operated of reversing said pulses before the code combination is transmitted, means to operate any desired set of said devices to reverse the 2'2 electrical character of corresponding impulses in a given number of successive code combinations to thereby encipher a message, the corresponding impulses in all successive code combinations continuing to be reversed until a different .set of ciphering :devices is operated, and means responsive to the occurrence of certain Baudot code combinations to restore said selected devices to normal andnncrate adifferent set of said devices to reverse a different plurality of pulses in a different number of succeeding code combinations.

'14. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, devices individual to each ofv the five pulses comprising the Baudot code and capable of reversing said pulses before the code combination is transmitted, means to operate a selected set of said devices to reverse the corresponding impulses in successive code combinations and thereby encipher a message, and means responsive each time certain Baudot code combinations occur to defeat control by the set of devices previously operated and to transfer pulse reversal control to different sets of said devices in succession, the time interval between such successive shifts of reversal control arbitrarily varying in accordance with fortuitous recurrence of said certain Baudot code combinations,

15. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, means whereby the sender may at will encipher a message by causing the reversal of the electrical character of any desired one of the pulses of each of a number of successive Baudot code combinations before the code combination is transmitted, the same corresponding pulse whether marking or spacing being always reversed in all successive code combinations until a difierent ciphering reversal is set up at the will of the sender, and means operating thereafter to cause the reversal of another pulse in each of a different number of successive Baudot code combinations.

16. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, means whereby the sender may at will encipher a message by causing the reversal of the electrical character of any desired one of the pulses of each of a number of successive Baudot code combinations before the code combination is transmitted, the same corresponding pulse whether marking or spacing being always reversed in all successive code combinations until a difierent ciphering reversal is set up at the will of the sender, means operating thereafter to cause the reversal of another pulse in each of a different number of successive Baudot code combinations, and means at a receiving station operating on a particular pulse of a Baudot code combination which is reversed at the transmitting station to restore said pulse to normal and thereby to cause the corresponding character or other signal to be received in deciphered form.

17. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, means whereby the sender may at will encipher a message by causing the reversa1 of the electrical character of any desired set of pulses of each of a number of successive Baudot code combinations before the code combination is transmitted, the same corresponding set of pulses whether marking or spacing being always reversed in all successive code combinations until a different ciphering reversal is set up at the will of the sender, and means operating thereafter to cause the reversal of another set of pulses in each of a number of successive Baudot code combinations.

18. In a secrecy system, means to translate messages into Baudot code combinations representing characters and other signals to be transmitted, means whereby the sender may at will encipher a message by causing the reversal of the electrical character of any desired set of pulses of each of a number of successive Baudot code combinations before the code combination is transmitted, the same corresponding set of pulses whether marking or spacing being always reversed in all successive code combinations until a different ciphering reversal is set up at the will of the sender, means operating thereafter to cause the reversal of another set of pulses in each of a number of successive Baudot code combinations, and means at a receiving station operating on a particular pulse of a Baudot code combination which is reversed at a transmitting station to restore said pulses to normal and thereby to cause the character or other signa1 to be received in deciphere-d form.

ERNEST OSMOND GAMMELL. 

